[PATCH] alsactl: Skip restore during the lock

[Takashi Iwai]

On Fri, 11 Dec 2020 17:45:45 +0100,
Jaroslav Kysela wrote:
> 
> Dne 11. 12. 20 v 9:38 Takashi Iwai napsal(a):
> > Currently alsactl-restore tries to initialize the device when an error
> > is found for restore action.  But this isn't the right behavior in the
> > case where the lock is held; it implies that another alsactl is
> > running concurrently, hence you shouldn't initialize the card at the
> > same time.  The situation is found easily when two alsactls get
> > started by both udev and systemd (note that those two invocations are
> > the designed behavior, see /usr/lib/udev/rules.d/78-sound-cards.rules
> > for details).
> > 
> > This patch changes load_state() not to handle the initialization if
> > the locking fails.
> 
> The operation should serialize in this case (there's limit of 10 seconds which
> should be enough to finish the initialization). The state_lock() function
> should return -EBUSY when the file is locked (and I'm fine to change the
> behaviour from 'init' to 'skip' for this lock state).
> 
> It seems that -EEXIST is returned when the lock file exists, but the
> open(file, O_CREAT|O_EXCL, 0644) caller has not enough priviledges to access
> this file when another user owns the file.
> 
> But alsactl from /lib/udev/rules.d/90-alsa-restore.rules and
> /lib/systemd/system/alsa-restore.service should be run as root, right?

Yes, it should be root.

I also wondered how EEXIST comes, too.  Maybe it's also the race
between the first open(O_RDWR) and the second
open(O_RDWR|O_CREAT|O_EXCL)?  If so, it'd be better to go back again
to the normal open(O_RDWR)?


thanks,

Takashi